drm/i915/display: Use platform check in HAS_LT_PHY()

drm/i915/display: Use platform check in HAS_LT_PHY()

NVL uses the Lake Tahoe PHY for display output and the driver recently
added the macro HAS_LT_PHY() to allow selecting code paths specific for
that type of PHY.

While NVL uses Xe3p_LPD as display IP, the type of PHY is actually
defined at the SoC level, so use a platform check instead of display
version.

Bspec: 74199
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Dnyaneshwar Bhadane <dnyaneshwar.bhadane@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patch.msgid.link/20251202012306.9315-7-matthew.s.atwood@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>